1. Field of the Invention
The present invention relates to a method for calibrating scales having a weight-determining weighing system with a processor-controlled computer and with a memory unit for storing information regarding gravitational acceleration (g).
2. Background Art
In connection with scales with a weighing system for determining weight, wherein the mass of an object is determined by its weight caused by gravitational acceleration and its effect on a sensor, the basically occurring problem is the dependence of the value of the gravitational acceleration on the location where the scales have been placed or are being operated. For example, the value of the gravitational acceleration varies between 9.797 and 9.825 m/s.sup.2 within the range of the European Community from approximately 70.degree. to 35.degree. north latitude. The value of the gravitational acceleration is further affected by the distance of the location where the scales are placed or operated from sea level or mean sea level (MSL). However, this effective value is of lesser importance; it is often neglected or taken into consideration in the calculation by means of the product of a correction factor, which is a function of the north latitude of the location, and the height above MSL.
The problem can be addressed by either determining the location of the scales and calculating the local gravitational acceleration from this or taking it from a memory or data bank, or calibrating the scales by means of weights directly at its location. The detected value of the gravitational acceleration is stored in a memory unit of the scales and is appropriately processed during weighing in the course of the operation of the scales.
In DE 44 08 232 A1 it has already been proposed to provide a satellite receiver circuit in a correction device inside the scales, which determines geographic position data by means of received satellite signals, then calculates a correction value and displays a weight result corrected on the basis of the correction value. For a position determination by means of the so-called GPS (Global Positioning System) the error-free reception from at least four satellites is required, which means that a direct visual connection with these four satellites must be provided. Reflections, i.e. multiple receptions, because of mountains or buildings can degrade the reception and can even make it impossible. It is practically impossible to perform the correct calibration of scales when in a mass of houses. A further disadvantage of the known system is to be seen in that, because of the time cycle in which the GPS signals are transmitted at present, 12.5 min are required, even with a clear visual contact with the satellites, for determining the location information. The manufacture of a scales is made not inconsiderably more expensive by the installation of a GPS system.